The present invention relates to electro-mechanically powered radio frequency (RF) transmission devices and, more particularly, to piezo-powered RF transmission devices that can send coded signals to a receiver or to a plurality of receivers.
One control circuit employing a piezo-electric transducer is described in U.S. Pat. No. 4,612,472 which discloses a remote controlled toy that utilizes a piezo-electric transducer in a hand-held transmitter to produce an RF signal. The toy vehicle, a cross between a machine and a dinosaur, does not transmit any signals, it only receives them. Upon application of a force on the top of a (blind) transmitter head, a slide element forces a striking element in the hand-held transmitter which is subsequently forced against the piezo-electric transducer causing a current to be generated. The current is fed to the contact point where a spark jumps across a spark gap to an antenna. The spark, in jumping across the spark gap, causes the RF signal to be transmitted from the antenna to the receiving antenna of the toy vehicle where drive motor is turned off and on by consecutive spark signals.
Another control circuit employing a piezo-electric transducer is described in U.S. Pat. No. 4,713,660 which discloses an electronic key that transmits a signal to an electronic lock. The electronic key has a power source which could be either a piezo-electric transducer or a solar cell. The power source charges a capacitor through a diode, which is used as the voltage source for all the electronic components of the electronic key. The electronic key uses a crystal oscillator (a piezo-electric element) to send a signal to a capacitor and then to a coil which functions as an antenna. A unique signal is generated by the electronic key through the use of a plurality of different resistive elements and a signal generator having a plurality of different timing periods. The lock includes a coil which acts as an antenna and a capacitor connected in parallel to the coil. The coil is the same value as the transmitting coil of the key 10 and is designed to receive the signals from the key.
Yet another control circuit employing a piezo-electric transducer is described in U.S. Pat. No. 4,937,581 which discloses an identification system used for identifying moving objects, such as railroad cars, from a remote interrogation station includes an information and identity storage device mounted on the railroad car and at least one interrogation station, located close to where the railroad car would pass. Upon being triggered by a signal from the remote interrogation station, the transmitter on the information and identity storage device, transmits stored data, such as the railcar's owner and identity, to the remote interrogation station. Power for the transmitter is provided by a power source, such as a piezo-electric material. A mass is mounted on a resilient strip that has the piezo-electric material bonded thereto. Vibration of the railcar causes movement of the mass which in turn deflects the resilient strip and piezo-electric material which generates an alternating voltage. The alternating voltage is rectified by diodes and stored in capacitors. The interrogation station, in addition to as sending a trigger signal, also sends a programming signal to the information and identity storage device in order to change or add information to the stored data residing in the information and identity storage device (i.e., bi-directional communication). Both the interrogation station and the information and identity storage device have a pair of antennas; one antenna for transmitting, and another antenna for receiving. A clock oscillator or watch crystal is used in the information and identity storage device for synchronization purposes when transmitting to the interrogation station.
What is needed but not provided by the prior art is a piezo-powered system that broadcasts a unique identification signal without the system being interrogated. Moreover, what is needed but not provided by the prior art is an identification system that automatically transmits a unique identification signal as often as a storage capacitor is charged to a predetermined minimum charge value needed for transmission by a piezo-electric element.